Validate that blocks satisfy either V1 or V2 PoW

[jrick]

This includes a port of dcrd's positional difficulty check. This check replaces
the check that difficulty bits match the expected difficulty when always
calculated using the original difficulty algorithm used since Decred launch.

The vote version has been bumped to enable voting on the new agendas.

This requires dependency updates in wire and blockchain/standalone in order to
create Blake3 PoW hashes and calculate the ASERT difficulty.

[davecgh]

I haven't tested this yet, but it reads correctly.

[davecgh]

I've tested this including both when simnet/testnet are forced active and by voting the agenda in on simnet. For the test involving voting the agenda in, I also tested for potential off by ones around the activation point.

Details:

I used the following dcrd and dcrwallet diffs in order to achieve the voting in the agenda on simnet:

dcrd:

diff --git a/chaincfg/simnetparams.go b/chaincfg/simnetparams.go
index cbd785d12..380ac11e1 100644
--- a/chaincfg/simnetparams.go
+++ b/chaincfg/simnetparams.go
@@ -460,7 +460,7 @@ func SimNetParams() *Params {
                                                IsNo:        false,
                                        }},
                                },
-                               ForcedChoiceID: "yes",
+                               // ForcedChoiceID: "yes",         // TODO(davec): Don't commit
                                StartTime:      0,             // Always available for vote
                                ExpireTime:     math.MaxInt64, // Never expires
                        }, {
diff --git a/internal/mining/mining.go b/internal/mining/mining.go
index 8e313938e..f473fcbb3 100644
--- a/internal/mining/mining.go
+++ b/internal/mining/mining.go
@@ -268,7 +268,7 @@ const (

        // generatedBlockVersionTest is the version of the block being generated
        // for networks other than the main network.
-       generatedBlockVersionTest = 10
+       generatedBlockVersionTest = 11 // TODO(davec): Don't commit

        // blockHeaderOverhead is the max number of bytes it takes to serialize
        // a block header and max possible transaction count.

dcrwallet:

diff --git a/go.mod b/go.mod
index e5ca79a7..363cd225 100644
--- a/go.mod
+++ b/go.mod
@@ -44,6 +44,7 @@ require (

 replace (
        github.com/decred/dcrd/blockchain/stake/v5 => github.com/decred/dcrd/blockchain/stake/v5 v5.0.0-20221022042529-0a0cc3b3bf92
+       github.com/decred/dcrd/chaincfg/v3 => ../dcrd/chaincfg
        github.com/decred/dcrd/gcs/v4 => github.com/decred/dcrd/gcs/v4 v4.0.0-20221022042529-0a0cc3b3bf92
 )

• From within the simnet harness, configure wallet1 to vote yes for the agenda:

wallet1$ ./ctl setvotechoice blake3pow yes

• Mine enough blocks via dcrd1 to reach just one block prior to the agenda activating and confirm the agenda isn't active yet:

dcrd1$ ./mine 1071
dcrd1$ ./ctl getblockchaininfo | jq -c '.deployments.blake3pow | {status,since}'
{"status":"lockedin","since":784}

• Nuke the existing wallet2 and create it fresh to test wallet syncing from scratch:

...
[INF] SYNC: Fetched 1103 new header(s) ending at height 1103 from wss://127.0.0.1:19566/ws
[INF] SYNC: Connected 1103 blocks, new tip block 41bac38323dab68493ae624b6d665fea7d70b7902b5426dc50a6c4fae1bd1978, height 1103, date 2023-06-07 15:19:46 -0500 CDT
...
[INF] WLLT: Rescanning block range [1, 1103]...
...
WLLT: Rescan complete
SYNC: Blockchain sync completed, wallet ready for general usage.

• Mine another block via dcrd1 to activate the agenda and confirm it's now active:

dcrd1$ ./mine
dcrd1$ ./ctl getblockchaininfo | jq -c '.deployments.blake3pow | {status,since}'
{"status":"active","since":1104}

• Confirm wallet1 and wallet2 are both at the activated tip:

wallet1$ ./ctl getinfo | jq .blocks
1104
wallet2$ ./ctl getinfo | jq .blocks
1104

• Mine another block via dcrd1 to activate the agenda and confirm it's now active:

dcrd1$ ./mine
dcrd1$ ./ctl getblockchaininfo | jq -c '.deployments.blake3pow | {status,since}'
{"status":"active","since":1104}

• Mine a couple more blocks via dcrd1 and ensure the wallets continue to vote and track the tip:

dcrd1$ ./mine 2
walllet1$ ./ctl getinfo | jq .blocks
1106
walllet2$ ./ctl getinfo | jq .blocks
1106